In recent years, for a slot machine using a rotary reel display unit, a liquid crystal display device has been suggested to invoke interest in a game while exhibiting a wider variety of images. In the slot machine, the liquid crystal display device is disposed in front of a reel and includes a backlight unit which is provided with a light guide panel and a light source disposed at the circumference of the light guide panel. The light guide panel is provided with a transparent window. Further, the transparent window is provided at a rear side thereof with a rotary reel having a symbol mark along a circumference thereof With this structure, a rotary reel display unit at a rear side can be viewed from a front side through the transparent window of the light guide panel and an image related to a game is displayed through the liquid crystal device on the front side, thereby invoking user interest in the game. However, as light fails to be radiated to the transparent window of the light guide panel of the gaming machine, the transparent window of the light guide panel becomes relatively dark and is distinguished from other portions of the display area of the liquid crystal display device or an image displayed through the liquid crystal display device can be blocked at a portion of the transparent window of the light guide panel. In order to solve such problems, the inventor suggested the provision of a sub-backlight unit including a second light guide panel and a second light source at a portion of a rear side of the backlight unit corresponding to the transparent window of the light guide panel (Korean Patent Application No. 10-2009-0102450). The problem of distinguishing the transparent window from other parts or blocking of an image can be solved by boosting radiation of light at a portion of the light guide panel corresponding to the transparent window using the sub-backlight unit.
However, the slot machine including a sub-backlight unit has a problem in that a reel at the rear side of the slot machine cannot be clearly recognized due to a pattern part of the second light guide panel disposed at a portion of the light guide panel corresponding to the transparent window. Further, as light emitted from the second light source disposed at the circumference of the second light guide panel is introduced into the light guide panel and reaches a surface of the reel disposed at the rear side thereof to be reflected forwards thereby, a symbol mark formed along the circumference of the reel cannot be clearly recognized due to the reflected light, causing deterioration in display quality.
Such a problem can also occur not only when a mechanical display device such as a reel, or a liquid crystal display device electronically realizing a reel is disposed at the rear side of the front display device, but also when an article other than the reel is disposed at the rear side of the front display unit.